Roof Drain Recession Plate

ABSTRACT

One embodiment of a recessed roof drain support (recession plate) is to be mounted under structural roof sheathing at the location of a roof deck penetration for a roof drain body. The roof drain body mounting flange, when mounted to the recession plate, will be below the surface of the roof sheathing, creating a recess for a roofing membrane to flow smoothly into the clamping surface of the roof drain body, leaving no opportunity for water to stand.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

FEDERALLY SPONSORED RESEARCH

None

SEQUENCE LISTING

None

TECHNICAL FIELD

This invention relates to roof drain apparatus in general, and more specifically to a supporting plate for mounting a commercial roof drain assembly, permitting the drain to be positioned beneath the level of the roof sheathing for optimum drainage.

BACKGROUND

A flat or nearly level roof is very common on large multi-occupancy and commercial buildings. In some situations the roof sheathing is plywood or structural material that in turn is covered by an impermeable roofing membrane. Because of the minimal slope on such roofs, roofers must install a sufficient number of drains penetrating the roof sheathing and the membrane that covers the roof. Most commercial roof drain assemblies have an outer flange to mount the drain assembly above the roof sheathing and an under-deck clamp to secure the drain body. A watertight seal is accomplished when the membrane is clamped between a drain compression ring and the drain body. With conventional installation practice the mounting flange of the roof drain assembly sits above the roof sheathing and the thickness of the flange creates a shallow dam around the drain assembly where the roof membrane rises above the level of the roof as it is sealed to the top of the roof drain. Even a small amount of standing water left after a rain can deteriorate the roof membrane around the drain and this often leads to leaks and structural failure. Standing water often freezes and damage can occur with the expansion of ice. Standing water on the roof deck can attract mosquitoes. Avoiding such disease vectors is very important.

Prior art has not adequately addressed the problem of standing water. Some prior art for roof drains have comprised drains fabricated from sheet metal. Other approaches incorporate mounting plates made of sheet metal with thin metal flanges that support commercial cast roof drains. Because these designs mount above the roof deck, none have successfully solved the problem of rainwater damming up around the edges of the drain.

Seitzinger, in U.S. Pat. No. 7,946,087 (2011 May 24) approaches this problem by providing a recessed sump in which to mount a commercial roof drain, the sump having a thin sheet metal flange to mount the sump from above the roof deck. This still leaves a shallow rise in the roof membrane surrounding the sump, additionally, the apparatus requires commercial fabrication involving either sheet metal presses or the welding and plating of multiple pieces of sheet metal to form a roof drain sump box. Field fabrication or modification would be cost prohibitive.

Logsdon, in U.S. Pat. No. 4,487,690 (1984 Dec. 11) uses almost the same design, with a flanged sheet metal stamping to support a commercial roof drain but also includes a stamped sheet metal clamping flange to hold the membrane to the drain support. Again, there is still a raised flange above the roof deck to collect water, and installation of the clamping plate doubles the installation time.

Murphy et al, in U.S. Pat. No. 5,882,043 (1999 Mar. 16) teaches a roof drain adapter primarily intended for poured concrete roofs with roof drains cast in place. However, many of the claimed features are adaptable to roofs incorporating wooden construction. Whether applied to wooden or concrete decks, three features may lead to failure of the roof integrity.

-   -   1. The roof drain is surrounded by a sheet metal apron         sandwiching the roof membrane between it and the roof sheathing.         The force needed to clamp the membrane is provided by multiple         threaded fasteners penetrating the apron, the membrane and the         roof sheathing. Each fastener penetrates the apron at the bottom         of a shallow trough. If one of these screws is not perfectly         sealed there will be leakage at that site.     -   2. In this implementation, both the apron outer region and the         apron fasteners would impede the flow of water on the membrane         upper surface. Best practice in roofing is to ensure that water         flows away from seams or fasteners. In any event both the apron         and the fasteners provide a source of leakage from capillary         action and freeze/thaw cycles.     -   3. Because the clamping ring is above the surface of the         membrane it will impede the flow of water into the drain,         forcing it to dam up until its level is high enough to flow over         the top of the clamping ring.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiment, a support for a roof drain assembly for flat roofs comprises a plywood mounting plate to be fastened on the underside of a plywood roof deck. This recessed mounting plate, hereafter referred to as a recession plate, has an opening to accommodate a commercial roof drain body, and positions it below the surface of the overlying waterproof roofing membrane, eliminating problems associated with accumulation of rainwater.

Advantages

The present invention eliminates the problem of a drain flange or support plate deforming the roofing membrane by mounting the drain body below the surface of the roof sheathing. Before mounting the roof drain assembly, the roof sheathing is cut out slightly larger than the outside dimensions of the roof drain body. The recession plate is then mounted under the roof sheathing at the site of the penetration, and the roof drain body is mounted onto the recession plate through the opening in the roof sheathing. With this procedure, the top of the drain body mounting flange will be recessed slightly below the roof sheathing so when the roof membrane is applied it will slope gently into the drain, leaving no opportunity for water to stand.

This embodiment uses inexpensive materials and low technology equipment to fabricate. It can be pre-fabricated in a workshop at very low cost. It can be quickly modified in the field by the installers. It can be installed in a fraction of the time required by prior embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a pre-fabricated recession plate.

FIG. 2 is a perspective view illustrating the recession plate being fastened to the underside of roof sheathing.

FIG. 3 is a perspective view of a recession plate installed on the underside of a section of plywood roof sheathing.

FIG. 4 is the same perspective view as FIG. 3 with the addition of a roof drain body oriented for insertion.

FIG. 5 illustrates a roof drain body after its mounting in a recession plate.

FIG. 6 illustrates the position of roofing membrane and roof drain clamping ring after clamping with machine screws.

FIG. 7 is a cross-sectional perspective illustration of a roof drain body mounted to a recession plate.

FIG. 8 is a cross-section of a commercial roof drain body mounted in a recession plate.

FIG. 9 is the detail view of FIG. 8 showing the area of the recession plate in relation to the roof sheathing and roofing membrane.

DRAWING REFERENCE NUMERALS

-   10 Roof Drain Recession Plate (recession plate) -   12 roof drain body -   14 roof drain body mounting flange -   16 marked cut line -   18 roof sheathing -   20 fastening screws -   22 roofing membrane -   24 roof drain opening -   26 roof sheathing penetration -   28 mating surface -   30 roof drain clamping ring -   32 clamping surface -   34 construction adhesive

DETAILED DESCRIPTION FIGS. 1-9—Preferred Embodiment

The preferred embodiment of my roof drain recession plate (recession plate) 10 is fabricated from exterior or marine grade plywood of at least 0.75 inch (24 mm) thickness. The dimensions of the recession plate 10 may be adjusted to accommodate different models of commercial roof drain body 12 and to fit the span between roof joists. At the center of the recession plate 10 an opening (roof drain opening) 24 is cut to closely fit the intended roof drain body 12, supporting it at its outer mounting flange (roof drain body mounting flange) 14. The mating surface 28 where the roof drain body mounting flange 14 contacts the recession plate 10 is coated with a plastic resin material compatible with the approved solvent or adhesive specified by the manufacturer of the roof drain body 12. During installation of the roof drain body 12 to the recession plate 10, solvent or adhesive is applied to the mating surface 28 shortly before placement. One or more marked cut lines 16 may be pre-applied to the surface of the recession plate 10 to facilitate modification for unusual conditions at the site of installation. Particularly, the recession plate 10 may be cut in two and the separate portions fastened in place separately through the roof sheathing penetration 26, eliminating the need to access the installation area from below the roof sheathing 18.

The recession plate 10 is fabricated with a roof drain opening 24 to allow a commercial roof drain body 12 to be fastened to it via the roof drain body mounting flange 14 at the time of installation. Before mounting the roof drain body 12, a roof sheathing penetration 26 is cut slightly larger than the outside dimensions of the roof drain body mounting flange 14. The recession plate 10 is then mounted under the roof sheathing 18, centered on the roof penetration 26. In the preferred embodiment, the recession plate is attached to the roof sheathing using both construction adhesive 34 and stainless steel flathead fastening screws (20). The roof drain body 12 is mounted into the roof drain opening 24 in the roof drain recession plate 10. Mounting of the roof drain body 12 is accomplished by applying adhesive or solvent at the mating surface 28 between the roof drain body 12 and the recession plate 10. In addition, under-deck clamps may be installed to the underside of the roof drain body 12, to clamp it to the recession plate 10.

With this procedure, the top of the roof drain body mounting flange 14 will be slightly lower than the roof sheathing 18 so, when the roofing membrane 22 is applied, it will slope gently into the roof drain body 12, leaving no opportunity for water to stand. 

I claim:
 1. An improved roof drain support plate which comprises: a. plywood or other structural material sized to fit between adjacent roof joists and; b. an opening in said plywood or other structural material sized to properly support a roof drain body by its mounting flange and; c. said roof drain support plate, hereafter referred to as a recession plate, capable of being fastened in a recessed position beneath a roof deck penetration; whereby the top surface of said roof drain body mounting flange, once installed, is below the top surface of said roof deck, so that when waterproof roofing membrane is applied over said roof deck and clamped to said roof drain body, said roof drain mounting flange will not impede the flow of water into said roof drain.
 2. The roof drain roof drain recession plate of claim 1 which further comprises; polyvinylchloride or other plastic surfacing on said roof drain recession plate in the area to which a plastic roof drain body would contact, such that said plastic roof drain body may be affixed with plumber's glue with solvent.
 3. The roof drain recession plate of claim 1 which further comprises fabrication using ¾ inch nominal dimension plywood or other like structural material.
 4. An improved process for installing a commercially manufactured roof drain which comprises: a. milling a roof drain recession plate from nominal ¾ inch plywood or similar structural material and sized to fit between adjacent roof joists and; b. milling an opening in said roof drain recession plate sized to allow attachment of a roof drain body by its mounting flange and; c. fastening said roof drain recession plate beneath a roof deck penetration; whereby the top surface of said roof drain body mounting flange, once installed on said roof drain recession plate, would be recessed below the top surface of said roof deck, so that when waterproof roofing membrane is applied over said roof deck and clamped to said roof drain body, said roof drain mounting flange will not impede the flow of water into said roof drain.
 5. The roof drain installation process of claim 4 which further comprises; applying polyvinylchloride or other plastic surfacing on said roof drain recession plate in the area to which a plastic roof drain body would contact and; affixing said plastic roof drain body with plumber's glue.
 6. The roof drain installation process of claim 4 which further comprises; clamping said roof drain body to said roof drain recession plate with threaded fasteners 